I have a 71 gtx and have had a driveline vibration problem forrrrever and could never figure out what was wrong. I posted a few threads on here already a while back about it but I got it down to being an engine problem.

The other day the vibration was nasty, so I went under the car and noticed both trans mount bolts were gone!!! Just gone. the vibration over a small period of time loosened them out all the way.

I went ahead and replaced the bolts with lockwashers and took it for a drive. Before starting off, I started the car and revved the engine up high, to about 3000rpms to get it warmed up. In doing so I noticed the vibration coming from the engine vibrating into the bellhousing just by sitting in park.

Took it for a drive, the driveline vibration with the tranny was gone since I replaced the bolts, but I could still heavily feel the vibration coming back into the bellhousing. This vibratoin occurs past 2500 rpms id say. I went on the expressway and the vibration goes away after about 4000 rpms. ???? I now understood that the reason the bolts came loose and why i always thought it was a tranny/rear end problem was because of the vibration that would occur since the bolts would loosen.

So, the problem???? Somewhere in the engine. I am going to replace my harmonic balancer soon and see if that does anything. Has anyone experienceed a similar vibration even in park, and if so any help???
Thanks

any help on finding the weights and how to determine what it needs? its a 340 by the way. and also the harmonic balancer has a counterweight behind it, about as big as the balancer. dont know if this is right. i bought a used one without the weight.

any help on finding the weights and how to determine what it needs? its a 340 by the way. and also the harmonic balancer has a counterweight behind it, about as big as the balancer. dont know if this is right. i bought a used one without the weight.

Not interchangeable.....

I would consult with a local engine machine shop or track it down on the net. Are you online????

I went ahead and replaced the harmonic balancer with a different one. The one previously on the car had the circular counterweight attached to the front of the balancer. The one I put in didnt. However, when i tried driving the car and gave it any gas at all the whole car would shake vigorously. Probably not the problem now I'm guessing because I was getting the same vibration coming in park when it hit the certain rpms.

have u tried to unbolt the converter and push it back and run the engine by itself and feel same vibration? dont take much to get to the converter..
p.s. if the converter is weighted, it wont work... the weight wont miss the flexplate blades.

I have the same problem in my ford 302 engine with an automatic transmision.I did change the damper and the flex plate and the problem still.I`m going to check the torque converter to see if the problem is a unbalance converter.I don`t know if you got an automatic trans or standard but in my opinion,you have to take off the damper and check without any belts and pulleys conected (for just a while)to see if your engine still shacking.This is to avoid any posibility to get the fan brocke or unbalance,problem with the water pump or generator loose.
Hope this help

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